The present invention relates to a facsimile transceiver utilizing an orthogonal data conversion process to increase the run length data compression efficiency.
In the present type of facsimile transceiver a scanning array which is typically of the charge-coupled-device (CCD) type comprises 32 photosensor elements arranged along a linear axis. The array is reciprocated perpendicular to the axis thereof to scan a rectangular portion of an original document. The photosensor elements produce sequential output data signals corresponding to incident light. After each photosensor element produces a data signal, the array is moved by an incremental distance perpendicular to the axis of the array and the photosensor elements controlled to each produce another data signal output. After each reciprocation of the array, the document is moved parallel to the axis of the array and the arry reciprocated again to scan another rectangular area of the document. This process is repeated until the entire document is scanned.
The data signals are subjected to run length compression and transmitted to a remote transceiver which reproduces the original document in response to the signals. The compressed data signals are expanded at the receiving transceiver and applied to a printing array comprising 32 printing elements such as electrodes which is moved in the same pattern as the scanning array to print the image pattern on a sheet of paper. Typically, the printing elements will induce an electrostatic charge pattern on the paper which represents the document. A toner substance is applied to the paper to develop the electrostatic image into a toner image which is fixed to the paper to provide a permanent reproduction of the original document.
Where the line density of the transceiver is 8 lines per millimeter, the width of the scanning array is only 4 mm. This is very small compared to the length of a typical original document such as a printed page of letter size, and the array must be reciprocated a number of times to scan the document. Such an arrangement enables the facsimile transceiver to be manufactured using a small number of components at low cost since only 32 photosensor elements are required. However, there is a disadvantage in that the run length compression efficiency is low. It has been determined experimentally that many short run lengths and therefore low run lengths compression efficiency results from such a scanning arrangement in which the photosensor elements are sequentially enabled to scan the document in the length direction rather than the width direction. Whereas the compression efficiency may be improved by providing a linear photosensor array of approximately 1728 elements (for A4 size original documents) having an axis parallel to the width direction of the original document and moving the document parallel to the array while sequentially enabling or strobing the array elements to produce data signals, such an arrangement is very expensive to manufacture due to the large number of photosensor elements and connecting circuitry.